我似乎无法访问 Android 中现有的 .db 文件。我已将文件 Zones.db 复制到\MyApp\app\src\main\assets 中，并创建了一个 DatabaseHelper 类，如下所示:
public class DatabaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
String DB_PATH =null;
private static String DB_NAME = "Zones";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
//<div style="display:none"></div>
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
//return cursor
public Cursor query(String table,String[] columns, String selection,String[] selectionArgs,String groupBy,String having,String orderBy){
return myDataBase.query("Zones", null, null, null, null, null, null);
}
和一个如下所示的 MainActivity 类:
public class MainActivity extends Activity {
Cursor c = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DatabaseHelper myDbHelper = new DatabaseHelper(MainActivity.this);
try
{
myDbHelper.createDataBase();
}
catch (IOException ioe)
{
throw new Error("Unable to create database");
}
myDbHelper.openDataBase();
Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_SHORT).show();
c = myDbHelper.query("EMP_TABLE", null, "_id=3", null, null,null, null);
if(c.moveToFirst())
{
Toast.makeText(MainActivity.this,
"_id: " + c.getString(0) + "\n" +
"ZONE_LETTER: " + c.getString(1) + "\n" +
"ZONE_NUMBER: " + c.getString(2) + "\n" +
"ZONE_TIME: " + c.getString(3) + "\n" +
"ZONE_PRICE: " + c.getString(4) + "\n" +
"PHONE_NUMBER: " + c.getString(5) + "\n" +
"COMPANY: " + c.getString(6),
Toast.LENGTH_LONG).show();
}
}
当我运行应用程序时，出现 no such table 错误，指出它无法在区域数据库中找到区域表。有谁知道如何解决这个问题吗？
最佳答案
尝试这个代码，它的工作完美，只需更改您的表名称和包名称
public class SqlLiteDataBaseHelper extends SQLiteOpenHelper{
private static final String TAG = SqlLiteDataBaseHelper.class.getSimpleName();
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_PATH = "/data/data/YOUR PACKAGE NAME/databases/";
private static final String DATABASE_NAME = "test1.sqlite";
private static final String TABLE_NAME = "Student";
private static final String COL_Name = "Name";
private static final String COL_ROLL_NO ="RollNo";
private Context context;
private SQLiteDatabase db;
public SqlLiteDataBaseHelper(Context context) {
super(context,DATABASE_NAME,null,DATABASE_VERSION);
this.context = context;
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
//This method is just retuning total no of recode in your table Getting single contact count
public int getDataCount() {
String userRollNo = null;
String query = "SELECT * FROM " + TABLE_NAME ;
Cursor cursor = db.rawQuery(query, null);
return cursor.getCount();
}
public void openDataBase () throws SQLException{
String path = DATABASE_PATH+DATABASE_NAME;
db = SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS | SQLiteDatabase.CREATE_IF_NECESSARY);
}
public void CopyDataBaseFromAsset() throws IOException {
InputStream in = context.getAssets().open(DATABASE_NAME);
Log.e("sample", "Starting copying");
String outputFileName = DATABASE_PATH+DATABASE_NAME;
File databaseFile = new File( "/data/data/YOUR PACKAGE NAME/databases");
// check if databases folder exists, if not create one and its subfolders
if (!databaseFile.exists()){
databaseFile.mkdir();
}
OutputStream out = new FileOutputStream(outputFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = in.read(buffer))>0){
out.write(buffer,0,length);
}
Log.e("sample", "Completed" );
out.flush();
out.close();
in.close();
}
public void deleteDb() {
File file = new File(DATABASE_PATH);
if(file.exists()) {
file.delete();
Log.d(TAG, "Database deleted.");
}
}
public boolean checkDataBase() {
boolean checkDB = false;
try {
File file = new File(DATABASE_PATH);
checkDB = file.exists();
} catch(SQLiteException e) {
Log.d(TAG, e.getMessage());
}
return checkDB;
}
}
在您的 Activity 中使用
sqlLiteDataBaseHelper = new SqlLiteDataBaseHelper(this);
try {
if(sqlLiteDataBaseHelper.checkDataBase()){
Log.e(TAG,"Data Base Already Exists");
}else {
sqlLiteDataBaseHelper.CopyDataBaseFromAsset();
}
}catch (Exception e){
e.printStackTrace();
}
try {
sqlLiteDataBaseHelper.openDataBase();
// after open data base u can read write data base
}catch (Exception e){
e.printStackTrace();
}
关于java - 如何访问 Android 中现有的 .db 文件？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37654803/